Preferred sports floors provide a high level of resiliency and shock absorption, and also preferably provide uniform play and safety to all participants. It is also preferred that sports floor systems maintain stability especially under changing environmental conditions.
A common sports floor system can be described as an upper playing surface attached to a subfloor structure, which is supported by resilient mounts. Often the upper playing surface is constructed of hardwood flooring. Sports floor systems such as these are disclosed in U.S. Pat. Nos. 4,879,875 to Peterson et al and 5,369,710 to Randjelovic et al.
The resilient mounts such as those described in the Peterson and Randjelovic patents are widely used in support of subfloor construction. The resilient mounts provide deflection as athletic impacts occur on the surface of the system. Most typically the resilient mounts are attached to the underside of subfloor panels such as plywood sheeting. The subfloor structure supported by the resilient mounts is not limited to plywood panel components and may include other components such as softwood sleepers or other suitable support material.
The sports floor systems previously described offer shock absorption to athletic participants. However, as these floor systems are free floating, there is no provision to assure proper contact of the resilient mounts to the supporting substrate. Free floating systems such as these, when installed over uneven substrates, may provide non-uniform deflection under athletic load, causing uneven shock absorption under impact. Also, the non-uniform reflection of the basketball off the floor creates a condition typically referred to as dead spots.
Further, free-floating systems are sometimes significantly affected by environmental conditions. Expansion of the wooden surface or subfloor typically occurs as high airborne humidity is absorbed into the wood, increasing the flooring moisture content. As wood moisture content increases, the flooring strip sometimes expands to create vertical pressure on floating sports floor systems resulting in what is commonly referred to as buckling. This occurrence creates a number of performance problems including inconsistent response to athletic and basketball impacts and especially safety concerns.
An alternative to free floating sports floor construction is the anchored sports floor systems. Examples of anchored sports floors are disclosed in U.S. Pat. No. 3,518,800 to Tank et al and U.S. Pat. No. 3,566,569 to Coke et al. The Tank patent includes specially manufactured metal clips to secure hardwood flooring strips to steel channels which are mechanically fastened to the concrete substrate. The Coke patent provides wooden nailing strips for attachment of hardwood flooring by nailing or stapling. The nailing strips are encased in steel channels mechanically fastened to the concrete substrate in the same manner as the steel channel in the Tank design.
Anchored systems provide integrity when fastening the subfloor steel channels to the supporting substrate. These systems also provide uniform play with consistent contact to the substrate regardless of undulations in the substrate surface. Anchored sports floor systems also maintain significant stability and buckle resistance under environmental conditions which can negatively affect free-floating sports floors.
However, unlike free-floating systems the anchored systems do not provide any significant degree of shock absorption and resiliency under athletic impacts. Providing shock absorption under athletic activities requires deflection of the floor system under load impacts such as when running, jumping or landing. The proper anchorage of floor systems such as those described in the Tank and Coke patents requires that the steel channel is secured to the concrete in a manner which allows very little deflection under athletic loads. It is known in the sports floor industry that minimal deflection must be maintained in anchored channel systems to prevent significant squeaking in these floor systems even under light athletic loads such as running, jogging or walking across the floor surface.
Sports floor systems such as U.S. Pat. No. 4,856,250 to Gronau et al and U.S. Pat. No. 5,016,413 to Counihan et al have been designed in an effort to obtain the advantages of both floating and anchored construction. These systems are typically referred to as resilient anchored sports floors. The Gronau and Counihan designs include structure, such as a steel channel, which allows downward deflection under athletic impacts while maintaining resistance to upward pressure such as those created by environmental influences as previously described.
The steel channel in both the Gronau and Counihan design is provided in manner which is intended to remain stationary regardless of downward movement of the floor systems. This feature prevents the possibility of squeaks which sometimes occur on typical anchored systems where the steel channel rubs against the anchoring pin when the system deflects. As with typical anchored systems, resilient anchored floors are intended to provide continuous contact to the substrate, thereby providing a higher level of consistency for shock absorption and ball reflection.
In systems made according to the Gronau and Counihan patents, the sleepers bear substantially all of the load applied to the floor surface. Moreover, these systems generally require a subfloor layer above the sleepers and below the floor surface. For these reasons, these resilient anchored systems do not provide ideal uniformity and reactions to impact.
In addition, substantial effort has been made in recent years to provide sports floor designs which control the width of deflection of the floor surface under athletic impacts. Such designs are intended to allow uninterrupted shock absorption for athletes performing in close proximity to each other. Athletic activities such as basketball and volleyball often cause participants to perform in close contact with other athletes during competition. This is especially true below the basketball backboard and along the volleyball net. Floor systems which allow a broad area of deflection under individual athletic impacts greatly reduce available deflection and consequently shock absorption for nearby participants.
Sports floor systems have been designed in an attempt to control the area of deflection under athletic impacts. An example of such a design is disclosed in U.S. Pat. No. 4,890,434 to Niese et al. The Niese design includes designated saw cuts in the underside of the subfloor sheeting and flooring material in an effort to control deflection. This design, as well as other subfloor configurations, provides greater flex in the floor system in an effort to specifically control the area of deflection under surface impacts.
Containment of impacts can be measured through testing, using the International Standard DIN 18032 part 2 for athletic sports surfaces. This standard is commonly used and specified for acceptable sports floor systems throughout the world. A measurement referred to as W500 is included in the DIN 18032 part 2 standard. This measurement is used to determine the deflection of the floor system at 500 mm from the point of impact on the floor surface. This test criteria allows evaluation of the floor systems ability to provide safety functions for individuals performing in close proximity to each other.
The W500 test standards have recently been changed to make them more restrictive. It is believed that the systems discussed above will not be able to meet these more restrictive deflection tests.